The present invention relates to a potentiometer combination according to the preamble of claim 1.
In many cases, a plurality of potentiometers, which sometimes must be operable from the outside, are required for certain control and regulating functions in electric machines, for example hand-held electric tools, stationary working machines, or the like. Frequently, these potentiometers are then mounted separately on circuit boards or printed wiring boards, and their shafts are accessible through an opening in the housing, if and to the extent they must be adjustable from the outside.
The special embodiment described hereafter concerns a speed control and regulating module for electrically driven machines, for example hand drills, saws, grinders, or the like. A module suited for such devices comprises usually a setting potentiometer that can be adjusted (continuously) from the outside by means of a set wheel or another actuating element, for adjusting the potentiometer to given values, depending on the desired power output and speed. However, such a module requires in addition a balancing potentiometer, for example for adapting the module to the device to be controlled and the electric motor driving it, or for other reasons, for example for performing temperature adjustments, or the like. It should be noted that the present invention relates, preferably, to such applications although it is understood that it is by no means restricted to them.
Such modules then comprise several potentiometers which are mounted on a common circuit board or else at different points and which are used in part for adjusting or balancing functions, and in part for adjustments to be performed by the ultimate user, even after final assembly of the device, for example for presetting a desired speed (as set-point value). Quite apart from the fact that much space is required for arranging a plurality of potentiometers, any balancing of the existing trimmers or adjusting potentiometers has to be carried out on the finished module while it is not possible to perform any balancing maneuvers on the completely mounted device as the respective circuit boards are arranged inside the housing of the device and any balancing (or rebalancing) operation, for example when the completely assembled device is to be finely adjusted after assembly, can be carried out only by opening the housing and removing the circuit board, unless openings are admitted in the housing of a device which give access to the respective trimming or adjusting potentiometers. However, such openings must then be closed again, or else they would provide the risk of contamination by foreign particles or dirt particles produced during operation of the respective machine.
Now, it is the object of the present invention to design a potentiometer combination mounted on a circuit board in such a manner that a space-saving structure and at the same time easy accessibility of the balancing potentiometer is achieved so that subsequent adjustments are rendered possible after complete assembly of the device, in addition to the normally required regular adjustments of a given variable of the machine.